Shrouded tail rotor



Sept. 2,1952 J. :5. LEE 2,609,053

SHROUDED TAIL ROTOR Filed Oct. 51, 1946 JOHN 6. LEE

,INV'ENTOR BY M K M ATTORNEY Patented Sept. 2, 952 1 11 2,609,053

2309.0'5'3 sanctions TAIL ii-orbit.

*I'iili'n G. Lee, l arniington, "Cam, assign'or *to United Aircraft Corporationg 'Eas't Hartford, flonii-tga corporation of Delalvvai-e v Application October. 31, iseaisetiei'lise.1706372 riso- PAT aNr or ies This invntion'relait'es to impreveatnrest eenef'ati'n'g meansfor aircraft; andmo're' particularly to controls 'for'helicopt'ers or the like including a control rotor which m'ay als'o functionto counterbalance the" torque of a second rotor," as required. In "helicopters known'asthe "single rotor type, asustaining rotor" provides sustentatio'n'a'nd propulsio'n, and "an auxiliary, 'or't'ail, rotor "balances the torque of "the sustaining rotor and also provides directional control. The proportion of power used "by the two rotors maywary widely, but for nibstpurpqses the tail rotor *me use fromapproxiiriately five to twelve percent of the total power of'the engine. With a twohundred horsepower-engine, the tail "rotor may absorb from tehto twenty five horsepower. The time that most "power is *iised is at takeofi fat zero air- 's'pee'd. Accordingly the useful load of a helicopter must be reduced from the maximurnload that can be supporteci-in flight, when less power is required to balance torque, because the tail rotor uses a largefportionofthepower available at takeoff. With "the -pres'e'n t invention the saving power to the torque balancing rotor 'gives a greater useful load. g V V A feature of the invention is that the percentage of "power requirements'of the tail rotor isreduced- 'substanti'ally. "'suehreature is obtained'by providing a (surface, or "shroud, around th tail rotor. The" shroud may'be'of "variable capacity, 6' "ithef rot'or "may "be variable capacity, or both may begjforontrol purposes.

YWiththe above feature; several other advancages ma be "had, "for example, "a smaller tail rotor m'aybe' used," or a "slower-speed for the tail rater may be" employed, the shroud wilyprdteot personnel, more' coihpact' cbhtfols become practicable, and many others.

Herie'e; an object of this invention is to;provi'de an} mproved rotor for 'a helicopter, or the" like, andir'n'pfdvedcoiitfols'therefor.

Other objects and advantages lie in the construction and arrangement of parts, and will be either obvious or pointed out in the following specification and claim.

In the drawings, 7

Fig. 1 is a diagrammatic elevational view of a helicopter including one form of my invention;

Fig. 2 is a partial sectional view taken on the line 2--2 of Fig. 1;

Fig. 3 is a side view of another form of the invention; v

Fig. 4 is a partial sectional view taken on the line 4--4 of Fig. 3;

Figs. 5, 6, and 7 are partial sectional views of three other modifications, and

4 mm. (01. ire-135.22)

12 "Figs. "Band 9=are elevational'andsectionalviews respectively "of another modification.

Referring more indetail to the drawings, and first to Fig. 1,a'helicop'ter"bodyl0 supports an engine l2"for turning a sustaining rotor Manda torque compensating rotor 16 through j-suitable transmission mechanism, "for example, "a drive shaft. The"sustainingro'tor'maybe of any type Suitableforp'r'oviding for "lift of the body 'IWand parts 'connected therewith, and may also provide for propulsion ofthe helicopter. The invention herewith is not limite'd'toany'specificisustaining rotor or means of propulsion but ismore concarried with providing an" improved thrust "producing 'rotor such as indicated by the "reference character It.

'With'powe'r supplied to the main-rotor from the engine l 2 there will be a'i'torque force tending to rotate the body lflina direetionppposite to the direction of rotation of the "rotor M. 'The rotor 16 is 'a'r'rangedto 'counte'ra'etthis tendency ofthe "body to to rotate and 'furthe'r'provide Iii rectional control for the helicopter. By wayof example, pedals 20 ma be us'e'dto'position'cables 22 to'va'r'y the-pitch of blades throughacontrol'i'necha'nism 2B whichma'y be substantiallyt'of the'ty'pe disclosed in theipaterit'of'LI. Sikorsky Np. 2.313260. y

Irford'er to reduce the power 'r'equi're'm'entsjof the rotor I 6 to 'a'mi'nimum withinpr'actical'.liniits and to provide "an, improved tail rotor structure better "adapted to 'yawing 'fii'ght, I, provide 'fa shrou 2's 'ar'ou dthe path bf the tips fo'fjithe blades '24. The shroud '23 may be shaped with a smoothly curved inlet 38'a'n'd a throat 32th direct air-into the tips of the bladesl l. vThe"shi"oud-2i3 should'haveas little "clearance as possible "betweenits internal diameter and "the external diameter of the v propeller; however, the internal surface "thereof forms a duct for a distance 'upstream anddown'stream of the pro'peller. shroud "may have an exterior surface shaped to reduce turbulence losses during forward flight to a minimum. Air is drawn into the shroud in the direction of the arrows in Fig. 2 and flows at a high velocity over the curved surface 30. Such fiow will cause a low pressure to exist at the surface 30 and a thrust T-l to be exerted by the shroud. The thrust T-l will augment thrust T-2 exerted by the blades 24. It has been found that a thrust gain of substantially twenty percent is obtained by a structure such as described. Accordingly it becomes possible to reduce either the power required by a conventially sized rotor, or to reduce the diameter of the tail rotor and expend the same power.

The

thorns 40 for turning a rudder 42 to provide for additional directional control for the helicopter. It will be understood that any suitable proportion of control may be assumed by the blades 24, shroud 38 and rudder 42 to obtain the best results for any given helicopter. The exact proportion of these parts may best be left to the mechanics skilled in the art for use Withdifferent sized craft.

In Fig. 5, a modified form of shroud 44 is connected by a pivot 46 to a tall 48 of a helicopter. The tail rotor blades 24 may be of the fixed pitch type if desired or of the variable pitch type to provide for additional control. For most control purposes it is possible to vary the position of the shroud 44 by actuating cables 53 connected with suitable manual controls, not shown, at one end, and to horns 52 at the other end to rotate the shroud 44. Movement of the shroud 44 will vary the efiective thrust of the shroud and hence vary the total thrust-rotor combination. Furthermore, movement of the shroud 44 will have a rudder effect to further control the heading of the helicopter. Any suitable proportions for the shroud may be used to obtain the most desirable action for any given helicopter.

Fig. 6 shows a shroud 54 associated with rotor blades 24 for producing thrust. The total thrust of the shroud-blade combination may be controlled by moving a sleeve 56 in and out of the interior of the shroud 54 to vary the length or extent of the shroud thereby extending the duct defined by the shroud and varying the thrust of the shroud-rotor combination.

Fig. 7 shows a modified means of varying the total thrust of blades 24 and a shroud 58 comprising hinged panels 66 which may be moved toward or away from each other to more or less restrict the duct defined by the shroud 58 to varythe velocity of the air issuing from the blades 24 and furtherto vary the effectiveness of the shroud 58 in generating thrust. The configuration of the duct defined by the shroud including its panels 66 may be controlled by manual means, not shown, in any convenient manner such as by cables or rods.

Figs. 8 and 9 show another means for further varying the shape of a shroud 62. An expansible tube, which may be 'made of live rubber, is mounted between the exterior of the shroud 62 and a flange 66. A control tube 68 may connect with a manually controlled valve from a source 4 of fluid pressure, not shown, which can supply or vent fluid to the tube 64 to expand or contract the same. As the tube 64 is expanded its component of thrust will be increased and as it is contracted this component will be decreased.

While I have shown and described different modifications for practicing my invention, obvi- 'ously other modifications and different arrangements of the modifications shown and described will occur to those skilled in the art. For this reason I wish not to be limited in my invention only to those forms shown and described but by the scope of the following claim.

I claim:

In a helicopter having an elongated body, a main sustaining rotor located in the forward portion of said body which exerts a torque tending to rotate said body about the main rotor drive shaft, an anti-torque rotor located in the aft portion of said body and rotatable about an axis transverse to said body for accelerating air to produce a lateral thrust acting on said body to oppose the torque of said main rotor, and means for increasing the thrust of said anti-torque rotor comprising an annular shroud surrounding the blade tips of the rotor, the shroud including inner and outer telescoping members, said outer member having an outwardly flared annular lip portion on th side of the advancing air which merges into an axial portion Of uniform diameter terminating on the side of the retreating air, and said inner, telescoping member having an'axi'al sleeve portion of uniform utside diameter'olos'ely receivable within and slidable axially along the axial portion of said outer member into games:- tended position in which it projects beyond said outer member on th side of v.the' latter opposite said lip portion.

JOHN G. LEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date 

